Wombat had some good suggestions...
My girl also feels the same way as BigRugbyMan. I just heard about it a few months ago, and I cannot say I was disappointed.
Anyway, I don't think it's as easy to accomplish as some people make it out to be. That's unless you or your girl just happen to have female friends who are also into the same lifestyle...then pulling in a 3rd party may not be very difficult. 'Course, then you have to deal with possible "weirdness" down the road if the 2nd chick & you & your girl are not all relaxed & carefree about it.
My g/f & I tried the strip club hangout deal, and I've never dropped so much $ in two straight months in my life! We had a couple of close calls, or almosts, but when it comes down to it strippers are always out for money. They'll tell you whatever bullshit to get another dance or two outta you, then flake out come the "afterparty". We've tried about 3 different clubs, all with the same results. My girl has gotten a little collection of phone numbers, but some aren't that hot, others have excess baggage & yet others are just total flakes.
My g/f ALWAYS gets asked if she's a new dancer, so we're not an unattractive couple. The only success so far was found online. It didn't turn into a 3-some since there was another couple involved, but the girls got it one while us guys watched, then we coupled-up. Not
exactly what we wanted, but it made for a f'ing hot evening.
Things to watch consider if searching online:
1) There are LOTS of bullshitters out there who are more likely to scam you than anything (i.e. lonely, ugly, hairy bastards hoping to trick women into sending their nudie pics). Require various photos first (in different surroundings, nude/clothed) and better yet, a phone conversation w/your girl right off.
2) There are THOUSANDS of the "Couple Seeking Bi-Female" listings out there. Your chances are much better having your girl post a "Woman Seeking Woman" ad and going from there. You'll get more responses and unsolicited messages.
3) Make the first meeting in neutral location (i.e. bar, club, etc.). See if the attraction is there between you all before getting into a potentially uncomfortable situation.
Wombat's suggestions were good, and definately set ground rules BEFORE any encounters. Who can do what to whom, what's off-limits, and don't cross the lines drawn. Determine if fucking some other chick is worth risking your current relationship for...that's IF your g/f says no-no to it.
BigRugbyMan - if your g/f has a few girls in mind, then can we assume that she
knows these girls are at the very least bi-curious? If she doesn't know it, then it can be quite difficult for your girl to breech that topic...I know it is for mine. Unless she knows for sure or she's asking a stripper, she won't discuss it for fear of embarassment if the chick is like "WTF?"
There are bound to be girls with the same curiosity at Tech, but unless you or your g/f know some of them or you search at a strip club or online, then they're not very easy to find. Web sites can be very useful, you just need to be aware of the issues I mentioned above.
Good luck. Know this was long, but I posed a question about this a few months ago when my girl let me in on her desires, and most of the posts I received were dumbass or smartass comments. You fuckers!
Oh yeah, some sites:
http://www.adultfriendfinder.com
http://www.iwantu.com
http://www.justbi.com (for your girl)
http://www.swingersingles.com (I think)
Please Scroll Down to See Forums Below 
I'm not a lesbian OK
No seriously TripleV why the hell are you living in Ottawa, I have a cousin working for the federal gov there and the only thing I heard from him was: damn this city is so boring.... Thats why I'll pray not to be sent by the RCMP in Ontario lol
